December 5, 1848

For months, starting in the summer of 1848, rumors of gold in the newly claimed territory of California filtered back to the eastern United States. Newspapers printed reports of rivers “paved with gold,” and a small trickle of eager prospectors were already journeying west. But on December 5, 1848, that trickle turned into a flood. “The accounts of abundance of gold are of such an extraordinary character,” President James K. Polk announced during his State of the Union address that day. These words kick-started the California Gold Rush, one of the largest migrations in U.S. history.

Earlier that year, the U.S. gained the California territory as a part of the Treaty of Guadalupe Hidalgo, which ended the Mexican-American War. At the time, only around 160,000 people — mostly Native Americans — lived in California, but by the mid-1850s, some 300,000 miners were working in the territory’s goldfields. Unfortunately, most were disappointed: The trip out west was brutal (whether overland or by sea), the job was tough, and there wasn’t enough gold to go around. Still, the gold-fueled migration transformed the West Coast. Once the gold fever broke, the Golden State had joined the union, San Francisco had grown from a frontier outpost to bustling city, and the U.S. now stretched from sea to shining sea.